The D.C. Police Department called it an isolated incident and said there was no active threat to the public.

Both the House and the Senate are in recess this week.

With members of Congress out of town, Capitol Police and the Sergeant at Arms had scheduled their annual “shelter in place” exercises for this week and next week, giving some staffers the impression that today’s lockdown was a drill.

A “shelter in place” drill was held this morning at the Capitol but the drill did not include the Visitor Center.